An additional billed amount that covers the difference between the power a customer expects to have available and the energy that the customer actually uses. Demand charges, occasionally referred to as capacity charges, are typically calculated based on the difference between a customer's peak energy use during a billing period and their nominal use (normal or hour-to-hour use) during the same period. If the customer expects to have substantially more power available to them than they actually use, then a demand charge is applied to cover this difference.

Demand charges are not a means of gouging customers by charging for unused energy. Instead they are a means of insuring that customers can have larger-than-normal supplies of energy available to them at a moment's notice.